Low back pain (LBP) produces major societal, industrial, and personal problems, resulting in substantial annual health care costs, lost productivity, and disability (Flicker et al., 1993, Spine, 18, 582-586). Only a small percentage of low back complaints can be diagnosed definitively (Nachemson, 1975, NINCDS, Monograph No. 15, US Department of Health, Education and Welfare) because current techniques are effective only for diagnosis of LBP associated with damage or abnormality of the skeleton. However, a substantial percentage of these complaints can not be diagnosed because existing techniques are ineffective for diagnosis of LBP associated with muscular dysfunction.
The importance of the muscular system in stabilising the lumbar spine is summarised in an article by Goel et al., (1993, Spine, 18, 1531-1541). The paraspinal muscles, in particular, have been shown to play a vital role in the stability and functional movement of the vertebral column but their role in spinal dysfunction is unclear. In this respect, reference may be made to studies in which it was determined that the lumbar multifidus (Kalimo et al., 1989, Ann. Med., 21, 353-359; Punjabi et al., 1989, Spine, 14, 194-200; Wilke et al., 1995, Spine, 20, 192-198) and the lumbar erector spinae (McGill, 1991, Spine, 16, 809-815; Soderberg and Barr, 1993, Spine, 8, 79-85; Sullivan, 1989, Phys. Ther., 69, 38-45) are important in stabilisation of the lumbar spine.
Instability of the lumbar motion segment which often manifests in the neutral zone motion, is implicated as an important factor in the development of recurrent and chronic LBP (Punjabi, 1992, J. Spinal Disord., 5, 383-389; Panjabi, 1992, J. Spinal Disord., 5, 390-397). In an article by Hides et al. (1994, Spine, 19, 165-172) reference is made to unilateral wasting of paraspinal muscles localised to one vertebral level in patients with acute/subacute LBP. Paraspinal muscle wasting also has been documented in post-operative patients (Laasonen, 1984, Neuroradiology, 26, 9-13; Mayer et al., 1989, Spine, 14, 33-36; Sihvonen et al., 1993, Spine, 18, 575-581) and in subjects with chronic LBP (Cooper et al., 1992, Br. J. Rheumatol., 31, 389-394; Tertti et al., 1991, Radiology, 180, 503-507).
The muscle system, through specific joint stabilisation strategies, can help minimise joint displacement, aid stress absorption and generally prolong the "cartilage serving time" of the joint (Baratta et al., 1988, Am. J. Sp. Med., 16, 113-122). Several muscle recruitment strategies have been implicated in the development of active joint stabilisation. In this respect, reference may be made to articles by Gollhofer and Kyrolainen (1991, J. Sp. Med., 12, 3440), Johansson et al., (1991, CRC Crit., Rev. Biom. Eng., 18, 341-368), Woo and Winters (1990, Multiple Muscle Systems, New York, Springer-Verlag), Hoffer and Andreassen (1981, J. Neurophysiol., 45, 267-285) and Johansson and Sojka (1991, Med. Hypotheses, 35, 196-203).
One strategy which is described in conjunction with joint stabilisation, is the early pre-programmed recruitment of particular muscles. These muscles are activated in anticipation of a prime mover of voluntary limb or trunk movement in normal individuals and are hereinafter referred to as anticipatory muscles. Pre-programmed muscle recruitment serves to ensure that the joint is supported prior to movement. For example, during a jumping task, the leg extensor muscles are recruited prior to ground contact (Gollhofer and Kyrolainen, 1991, J. Sp. Med, 12, 34-40).
In addition, activation of postural muscles has been shown to occur in anticipation of the prime mover of voluntary limb or trunk movement to prevent the inevitable disturbance to balance. In this respect, reference may be made to Belen'kii et al., (1967, Biofizika, 12, 135-141), Bouisset and Zattara (1987, J. Biomech., 20, 735-742) and Oddsson (1989, Acta Physiol. Scand., 136, 47-58).
Reference also may be made to studies by Cresswell et al., (1992, Acta Physiol. Scand., 144, 409-418; Cresswell et al., 1994, Exp. Brain Res., 98, 336-341) in which it was shown that the transversus abdominis (TA) is activated with all trunk movements regardless of the primary direction of movement and is recruited prior to all other abdominal muscles with sudden perturbations of the trunk. The preactivation of TA with self loading was considered to be a component of a feed-forward postural strategy to increase the stability of the trunk by increasing the stiffness of the intervertebral joints of the lumbar spine (Cresswell et al., 1994, Exp. Brain Res., 98, 336-341).
The aforementioned references highlight the importance of the muscular system, and in particular, the paraspinal muscles, in the segmental stabilisation of the lumbar spine and in preparation of the disturbance to balance. However, at present, it is not possible to measure directly the strength of individual paraspinal muscles in order to diagnose muscular dysfunction associated with LBP. As a consequence, imaging techniques have been used to measure muscle size, and the relative advantages of ultrasound imaging, computed tomography (CT) scanning, and magnetic resonance imaging (MRI) in rehabilitation have been presented (Stokes and Young, 1986, Physioth. Prac., 2, 31-36).
In an article by Hides et al., (1995, Spine, 20, 54-58) reference is made to a comparison of real-time (RT) ultrasonography and MRI in respect of measurement of lumbar multifidus cross-sectional area. In this study, it was reported that, in contrast to MRI, RT ultrasonography was less expensive and more widely accessible. However, it was also stated that excluding the measurement of large muscles, RT ultrasonography had the disadvantage of a relatively limited field of view and was unable to provide pilot sections for confirmation of vertebral levels when imaging the spine. As a consequence of these limitations, the authors suggested that strict protocols should be followed to allow accurate measurement of the soft tissues.
In a prior article by Hides et al., (1994, Spine, 19, 165-172), the effect of LBP on the size of the lumbar multifidus was examined using RT ultrasonography. This study showed that the localisation of multifidus wasting is likely to be due to inhibition of perceived pain via a long-loop reflex pathway. However, there was a lack of correlation between severity of paraspinal muscle wasting and symptoms. This lack of correlation highlighted the requirement for objective measurement of paraspinal muscular dysfunction in LBP.
Most techniques available currently to assess muscular dysfunction are either non-objective or they lack clinical validation and reliability. One technique that does provide objective data uses electromyographic (EMG) spectral analysis of lower back muscles. Although some prior EMG systems provided advantages over other techniques, these suffered certain deficiencies resulting primarily from treatment of individual muscle groups as a continuous muscle mass and exclusive reliance on the amplitude of EMG signals. In this respect, reference may be made to Gilmore and DeLuca (1985, IEEE Trans. Biomed. Eng BME, 32, 75-78); Roy et al., (Computer Aided Back Analysis System, IEEE Engineering in Medicine and Biology Society - 10th Annual International).
In U.S. Pat. No. 4,655,227 reference is made to a method and equipment based on analysis of EMG activities for the detection of mechanical injuries in the lumbar spine of a patient and the identification of the injuries, using a mathematical model applicable to the five lumbar vertebrae of a human being, and to their disc. This specification, however, did not disclose a method or an apparatus for diagnosis of muscular dysfunction.
Reference may also be made to U.S. Pat. No. 5,086,799 and 5,163,440 which respectively describe a system and a method for the detection of muscular dysfunction based on analysis of EMG activities in association with muscular fatigue.
Electromyographic studies have also been used in association with high resolution ultrasound to record the behaviour of the TA muscle relative to the external oblique (EO) and rectus abdominis (RA) in humans (Troyer et al., 1990, J. Appl. Physiol. 68, 1010-1016). These studies showed that TA is recruited preferentially to the superficial muscle layer of the abdominal wall (RA and EO) during breathing. However, these studies did not provide a correlation between the measurement of activation of TA and LBP.
Reference also may be made to an article by Di Fabio (1987, Phys. Ther., 67, 43-48) in which an EMG was used in concert with a computer analysis system (CAS) for the determination of the temporal sequence of muscle contraction. This study showed that when CAS was used for the detection of EMG muscle burst onset, it demonstrated perfect reliability and was superior to visual inspection of the data. However, this study was limited to the measurement of the temporal sequence of activation of four lower extremity muscles in response to unexpected balance perturbations and was not used for the analysis of lumbar muscular dysfunction associated with LBP.
From the foregoing, it is evident that certain techniques exist that are less than satisfactory for the effective diagnosis of LBP caused by neuromuscular dysfunction.